Abstract Current therapies to treat the orphan disease, catecholaminergic polymorphic ventricular tachycardia (CPVT), have potential side effects so severe that hospitalization is required upon treatment initiation, and severely exacerbate depression and fatigue in children that already have psychological issues due to this devastating, life-long, life-threatening illness. The long term goal of Elex Biotech is to create improved pharmaceuticals with minimal side effects, thereby providing superior treatment options for CPVT and related ventricular arrhythmias. In the current Phase 2 proposal the main objective is to obtain extensive pre-clinical data on optimized lead compounds. The central hypothesis is that drugs with enhanced electron donor properties that target RyR2 will be highly effective in decreasing the SR Ca2+ leak associated with ventricular arrhythmias. This unique hypothesis guided the development of lead compounds that met or exceeded phase 1 benchmarks, including one that was effective in treating CPVT in rodent models at nearly 4 orders of magnitude lower dosage levels compared to the current treatment standard flecainide as well as all other well- known RyR2 inhibitors such as K201. The specific aims addressing the Phase 2 objective are (i) to optimize lead compounds via an SAR evaluation based on in vitro and preclinical studies and (ii) preclinical evaluation of the lead drug candidates. One or more lead compounds identified in Aim 1 will be moved into in vivo preclinical evaluation. Additional leads will be tested and structural modification made to optimize performance based on screening such as liver microsomal stability, plasma stability, protein binding, secondary pharmacology screening (off-target effects), and in silico genotoxicity. A pharmacokinetic (PK) study in mice is planned to evaluate parameters underlying efficacy to guide dosages for toxicology studies, a PK study in rat. Acceptable results for bioavailability and half-life from th rat PK study will confirm a lead drug candidate to be moved into dose range finding studies (DRF) in Phase 3. The company has assembled a team with extensive expertise in cardiac ion channels, pediatric cardiology and CPVT, calcium channel biophysics, organic synthesis, medicinal chemistry, preclinical safety studies and orphan drug regulatory review.